426 SPORANGIOPHORIC PTERIDOPHYTES 
surface of the sporophyll. This is illustrated by the living Psilotaceae, 
and by some species of Sphenophyllum, notably S. majyus, which shows 
other characters held to be primitive. But it is departed from in 
S. Dawsont and S. Rémeri, where the number of the sporangiophores 
is in excess of the sporophylls, while the leaf-whorls are deeply webbed 
into a cup: C/ezrostrobus is also an exception, but there the three sporangio- 
phores correspond in position and number to the lobes of the tripartite 
sporophyll: this condition, together with the vascular connections, suggests 
a parallel amplification of the sporophyll and of the sporangiophore, to 
which we shall see modern correlatives later among the Ophioglossaceae. 
Thus, though liable to modifications, the characteristic position of the- 
sporangiophore in the Sphenophyllales is in a median position on the 
upper surface of the subtending bract. 
Here I must enter my dissent from certain “ interpretations” which 
have been given of the leaf-borne sporangiophore. In cases where it 
is inserted on the upper surface of the leaf, as in the Sphenophyllales, it 
has been designated a “ventral lobe.” If “ventral lobes” were of 
common occurrence on the vegetative leaves of these or of other Pterido- 
phytes, there might be some meaning in the term. It lies with those 
who use this expression to show that such “ventral lobes” exist normally, 
other than these spore-producing bodies which they so designate. If they 
do not normally exist, then calling a leaf-borne sporangiophore a “ ventral 
lobe” merely leads to confusion, and provides no explanation of its real 
nature. It introduces the idea that the sporangiophore is a result of 
“metamorphosis” of some pre-existent vegetative structure, of the nature 
of a “ventral lobe,” an opinion untenable in the absence of proof that 
such bodies existed in the vegetative state. 
But, on the other hand, it has been shown above that in the Equisetales, 
a series undoubtedly felated to the Sphenophyllales, parts similar to the 
sporangiophores of the Sphenophyllales in structure and in function are 
borne upon the axis and have no constant relation to the bracts: for 
reasons assigned above (p. 382, etc.) these are not themselves to be held as 
foliar. Study of such sporangiophoric types, not separately but collectively, 
thus leads to a conception of the sporangiophore as a non-foliar structure, 
which may be inserted either on the axis or on the leaf, though in certain 
groups it shows a regular relation to the latter. It is, in fact, a part sad 
generis as much as the sporangium is, and not the result of modification 
of any other part. 
The history of individual development of the sporangiophore, as traced 
in Zmesipteris and Fsilotum for leaf-borne types, and in LZgudsetum where 
they arise directly from the axis, gives a clue to their nature. The sporan- 
giophore first appears as a broad cushion of tissue, in the peripheral parts 
of which the sporangia are early initiated: these are from the first orientated 
outwards from the centre of the outgrowth. In the Psilotaceae (as also 
in S. majus) they maintain this, which. may probably have been their 
